NCIS Prequel 2 Episodes

Here are the 2 episodes from Jag that introduce NCIS

The body of a Navy Lieutenant JAG officer is found in the woods by a boy scout, and random test later confirm that the JAG officer was pregnant. Admiral Chegwidden informs members of JAG of the news when it's revealed that the body is that of Lt. Loren Singer.

Called into investigate the body, NCIS then launches an investigation into Singer's murder. Commander Rabb calls his half brother Sergei to inform him of Loren's murder. The episode is mainly dedicated to the investigation into Singer's murder, and finding a suspect. NCIS interviews several members of JAG, including Mac, Roberts, and Manetti.

After interrogating Rabb, Special Agent Leroy Jethro Gibbs reads him his rights, and places him under arrest for the murder of Lt. Loren Singer with Special Agent Tony DiNozzo and Viv Blackadder aiding him. This is where the first part of this two-part episode ends with the storyline later picking up in the second episode, "Meltdown".

On the side, NCIS is attempting to apprehend the terrorist responsible for the attack against the USS Cole and they interrogate another terrorist, Amad Bin Atwa, who helped finance the attack. Director Thomas Morrow wants Gibbs to take over the interrogation of Atwa so as to prevent another terrorist attack against a Navy ship.

"Ice Queen (NCIS spinoff, part 1 of 2)" April 22, 2003
Harm becomes the prime suspect when Lieutenant Singer, who has been missing for three months since leaving JAG, is found dead in a tree by a young boy scout searching his stray arrow and the evidence implicates his half-brother as the father of her child while Harm himself is believed to be responsible for Singer's murder.

"Meltdown (NCIS spinoff, part 2 of 2)" April 29, 2003
As the evidence mounts against Harm, only the efforts of the NCIS team may keep him out of the brig for life but with NCIS Special Agent Leroy Jethro Gibbs off trying to stop another terrorist attack, it falls to his colleagues Anthony "Tony" DiNozzo and Vivian "Viv" Blackadder to find evidence leading them to the real killer and stop Harm from being punished for a crime he didn't committ. Thanks to DiNozzo's efforts, it's soon discovered that the JAG team's old enemy Commander Theodore Lindsey is responsible for Lt Singer's murder, and he set Harm up as a measure of revenge.